Production of sodium nitrate



Patented 25, p 1928.

U TED .STATTES' 1,696,197 PATENT OFFICE.'

no'nnnazonrnssenon, or LUDWIGSHAFEN-ON-THE-RHINE, AND xurar norms, or

mauunnna, GERMANY, assronons TO I. G. rannnumnusrmn AKTIENGESELL- sewnon FRANKFORT-ON-THE-MAIN, GERMANY, a oonronnrrou or GERMANY.

PRODUCTION OF SODIUM NITRAIE.

No Drawing. Application filed September'22, 1927, Serial No. 221,394,and in Germany October 14, 1926.

, Thepresent invention relates to the recovery of sodium nitrate fromits aqueous solutions.

Hitherto, the recovery of sodium nitrate from dilute solutions, such asthose which are obtained inthe treatment of caliche, has been effectedeither'by cooling to a low temperature or by evaporation. A considerableex penditure of energy is necessary for carryin out either of thesemethods, which substantially increases the cost of the product thusobtained. j

We have nowfound that sodium nitrate may be economically recovered fromthe said posed dilute solutions by converting the sodium nitrate insolution into a double salt which may also beia mixed salt which is onlyslightly soluble at ordinary temperatures, and subjecting the same afterseparation from the liquid to a treatment suitablefor the production ofsodium nitrate. For example, the addition of solid sodium sulfate causesthe deposition of a double salt of the composition NaNQ .Na SO .H O(Darapskite),

and in this manner it is easy to precipitate, from a coldsaturatedsolution of sodium nitrate, per cent of the nitrate in the form of thesaid double salt, at ordinary tempera ,ture. In order to'recover theremainder of thefnitrate, the mother liquor left after the separation ofthe double salt is preferably employed for leaching-fresh quantities ofnitrate earth. The double salt may be decominto its two. components byheating it to above 70. C. with just the amount of \vater required fordissolving the nitrate containedj therein, the residual sodium sulfate.which is onlyslightly soluble inhot water. being separated by. hotfiltration. The sodium nitrate is easily recovered, in a solid j andpracticallypure condition, by cooling the solution.

The greater'portion of" the sodium sulfate required fortheprecipitationof the double salt is recovered when the latter is decomposed, and theremainder n'ray be recovered by strongly cooling the mother liquorremaining after the separation of the double salt.

vTheadvantage of the process according to the present invention.consists in the far smaller consumption of heat and energy, so thateven inferior grades of cahche for WillCll heat need be introduced intothe system in order to separate the nitrate in the form of the doublesalt. and only a limited supply of heat is required for the conversionof the double salt into its components. A substantial advantage over theinitially mentioned process of evapor'giting the aqueous solutions inorder to concentrate the same consists also in the fact that thesolutions to be heated in the treatment of the double salt are free fromchloride, so that the otherwise usual extensive corrosion of thematerial of the apparatus is avoided.

The following example will further illustrate the nature of the saidinvention which hovvever is not limited thereto.

Ezc llt;

To a solution of the kind obtained by leaching caliche at ordinarytemperature, and containing, per 1000 kilograms of Water, about 550kilograms of sodium nitrate, 37 kilograms of sodium sulfate and 240kilograms of common salt, 490 kilograms of anhydrous sodium sulfate, areadded gradually While \vell stirring at ordinary temperature. About 780kilograms of double salt are formed which are filtered off by suction.The mother liquor is cooled to about 8 C. Whereupon about 90 kilogramsof Glaubers salt separate out.

The decomposition of the double salt is effected, for example, in thefollowing manner.

1000 kilograms of the double salt are heated with 720 kilograms of astock solution containing about 87 kilograms of sodium nitrate and 59kilograms of sodium sulfate per 100 kilograms of water, about 70kilograms of 'ater being evaporated during the treatment. Theundissolvcd sediment consists of about 580 kilograms of sodium sulfate,which is separated while still hot. The filtrate is cooled to theordinary temperautre, whereby about 350 kilograms of sodium nitrateseparate out. The liquid obtained on filtration may be employed as thedecomposing solution for the next batch, Whilst the deposited sodiumsulfate is returned to the main proc ess.

What we claim is:

The process of recovering sodium niual sulfate being separated by hotfiltration and the sodium nitrate recovered by tooling the solution. 10

In testimony whereof we have hereunto Ft'l our hands.

, ROBERT GRIESSBACH.

KURT ROHRE.

